Sudden alarm.

Meaning: This means that the warning signal was unexpected and quick. It's like saying, The warning signal came out of nowhere and caught everyone off guard.

Choice of Words: Sudden is an adjective used to describe something that happens quickly and without warning. Alarm is a noun that refers to a signal or warning of danger. When used together, "Sudden alarm" describes a warning signal that happens quickly and without warning.

Alternative Expressions

The alarm was sudden.

Meaning: This means that there was a loud noise that happened unexpectedly and was meant to warn people about something.

Choice of Words: Was is a verb that is used to describe something that happened in the past. Sudden means happening or changing quickly or unexpectedly. Alarm means a loud sound that is used to warn people of danger or to wake them up. When you put them together, "The alarm was sudden" means that a loud sound happened unexpectedly and was used to warn people.

Related Expressions